It maybe that you need to land softer I know it makes the moves harder but its easier on the knee's. I had the same problem & started landing softer & the problem went away....remember Insanity is a high impact workout.
I have completed Insanity twice so let me know if you have any question.
Check out my thread for support too.
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Glucosamine would be good but I would try landing softer first before adding it.
talk with you soon, Carlie